Constituents of milk are known to control the rate of milk secretion and the extent of mammary development according to the frequency and completeness with which those constituents are removed through the demand of the offspring or the farmer's husbandry. Alternative methods of inducing milk secretion can be provided by mechanical means which reproduce the stimulus required to provide lactation. Such biochemical feedback mechanisms within the breast or udder act to modulate the lactation-promoting effects of mammogenic and galactopoietic hormones. The regulatory characteristics, albeit not all of the active factors in milk, have been described by studies on lactating ruminants at the Hannah Research Institute, Ayr, Scotland.
Mammary development, measured in terms of the number of parenchymal cells, is subject to control by local mechanisms activated by the frequency of milk removal during lactation. Circumstantial evidence obtained from milking studies in dairy animals suggests that this local control may also be regulated through feedback control by constituents of milk.